Electro-hydraulic actuators, such as those used in conjunction with fuel injectors having a direct control needle valve, rely upon relatively small and fast valves in order to control fuel injection characteristics. In one class of fuel injection systems, a direct control needle valve opens and closes the nozzle outlet of the fuel injector. The direct control needle valve is controlled hydraulically via a relatively high speed needle control valve that has the ability to apply either low pressure or high pressure to a closing hydraulic surface associated with the direct control needle valve. One such direct control needle valve and accompanying needle control valve is disclosed in co-owned U.S. Pat. No. 5,669,355 to Gibson et al. That reference teaches a fuel injector that includes a needle control valve with the ability to apply high pressure or low pressure oil to a closing hydraulic surface of a direct control needle valve. When high pressure is applied to the closing hydraulic surface, the needle valve stays in, or moves toward, its closed position to end the spray of fuel. When low pressure is applied to the closing hydraulic surface, and the fuel is at injection pressure levels, the needle valve will stay in, or move toward, its open position to allow fuel to spray out of the nozzle outlets of the fuel injector. In order to accomplish various goals, such as reducing undesirable emissions from an engine, engineers are constantly seeking ways of improving performance of direct control needle valves, especially by addressing problems associated with needle control valves.
One of the problems that could be addressed in improving a needle control valve is to reduce response time. This problem can then be broken down into seeking ways to reduce the valve member's travel distance, increasing the travel speed and/or acceleration of the valve member, decreasing the influence of fluid flow forces on valve member movement, and other issues known in the art. In addition, it is desirable to employ strategies that hasten the rate at which pressure changes can occur within the needle control chamber that applies the hydraulic force to the closing hydraulic surface of the needle valve member. These problems are further compounded by issues relating to an available space envelope for the valve, and maybe more importantly the ability to address all of these problems with a structure that allows for the valve to be mass produced with consistent behavior from one valve to another.
Still another problem that could be addressed relates to efficiency. For instance, reducing leakage through the valve can make a difference in the overall viability of a given valve. Leakage is potentially a problem since many valve assemblies include a valve body made up of several components that are attached or otherwise clamped together. For instance, a typical three way valve might include an upper seat component separated from a lower seat component by a valve lift spacer. These three components can be held together with four bolts distributed around the periphery of the valve body. While such a strategy can be successful, the areas needing the highest clamping loads are often located toward the center and well away from the periphery of the valve body. For instance, the valve assembly might have a centrally located valve member adjacent an annual sealing land defined by the contact area between the valve body components. Because these sealing lands can be subjected to relatively extremely high pressure differentials during an injection event, leakage through these sealing lands can be a concern. Therefore, the region around these sealing lands are in need of relatively high clamping forces in order to avoid leakage. Unfortunately, spacial constraints attributable to plumbing and other factors known in the art prevent, or at least inhibit, placement of clamping bolts closer to the areas where they are needed.
The present invention is directed to one or more of the problems set forth above.